1. Field of the Invention
The invention relates to a waterless power generator. More particularly, the invention pertains to an electrical power generator and process for producing electrical power with a fuel cell. The reaction of oxygen and hydrogen gases in a fuel cell produces electricity and by-product water, which by-product water is reclaimed and used to produce additional hydrogen gas through its reaction with a solid hydrogen producing fuel.
2. Description of the Related Art
Similar to batteries, fuel cells function to produce electricity through chemical reactions. Rather than storing reactants as batteries do, fuel cells are operated by continuously supplying reactants to the cell. In a typical fuel cell, hydrogen gas acts as one reactant and oxygen as the other, with the two reacting at electrodes to form water molecules and releasing energy in the form of direct current electricity. This direct current electricity may then be converted into an alternating current. The apparatus and process may produce electricity continuously as long as hydrogen and oxygen are provided. While oxygen may either be stored or provided from the air, it is generally necessary to generate hydrogen gas from other compounds through controlled chemical reactions rather than storing hydrogen, because storing hydrogen gas requires that it either be compressed or cryogenically cooled. As fuel cell technology evolves, so do the means by which hydrogen gas is generated for application with fuel cells.
Currently, there are various methods which are known and employed for generating hydrogen gas. One method is by a process known as reformation in which fossil fuels are broken down into their hydrogen and carbon products. However, this system is undesirable in the long term because it is dependent upon a non-renewable resource. Another means of generating hydrogen gas is by reversibly adsorbing and releasing hydrogen gas from metal hydrides or alloys through heating. While this method is useful, it is not preferred because the metal hydrides are typically very heavy, expensive and only release small quantities of hydrogen. Yet another means by which hydrogen gas is generated is through reactive chemical hydrides. This process involves chemically generating hydrogen gas from dry, highly reactive solids by reacting them with liquid water or acids. Chemicals especially suitable for this process are lithium hydride, calcium hydride, lithium aluminum hydride, sodium borohydride and combinations thereof, each of which is capable of releasing plentiful quantities of hydrogen. The disadvantages associated with this method is that reaction products from the chemical and liquid water typically form a cake or pasty substance which interferes with further reaction of the reactive chemical with the liquid water or acid. This method is also disadvantageous in that the storage of liquid water fuel consumes additional space and increases the overall weight of the associated power generator.
There is currently a need in the art for lighter weight and smaller sized power sources for applications such as portable electronic devices, wireless sensors, battlefield applications, and unmanned air vehicles. Presently, the power source that is most often used for portable applications is the lithium battery, which has a limited energy capacity as a function of volume and especially as a function of weight. It is desirable to increase the energy capacity of current power sources so as to decrease the power supply replacement interval and/or increase operating life, while also reducing the size and weight of the power source.
The present invention provides a solution to these problems. The invention provides an electrical power generator and a process for generating hydrogen gas for fueling a fuel cell. The electrical power generator comprises a waterless generator, utilizing only by-product water from a fuel cell as a water vapor fuel source and without the need for externally supplied water. More particularly, the invention provides an electrical power generator that consumes stoichiometric amounts of water vapor and substantially solid, non-liquid chemical hydride. The fuel cell is preferably initially loaded with a hydrogen gas to initiate a reaction at a hydrogen-oxygen Proton Exchange Membrane (PEM) fuel cell between the hydrogen gas and oxygen gas. This reaction produces water molecules which are maintained within the generator housing at a water retention zone that deters the diffusion of generated fuel cell water out of the housing. The water molecules then diffuse back into the power generator in the form of water vapor, which water vapor is then reacted with the chemical hydride to produce more hydrogen gas. This generated hydrogen gas is then used as a fuel which allows the fuel cell to generate additional electrical power and additional water. By reclaiming and recycling this by-product water, the need for stored water is eliminated, thereby reducing the overall size and weight of the system, as well as increasing the energy density, specific energy and current capacity of the system. Further, by reacting water vapor with the aforementioned solid chemical substance, it has been found that the typical problems associated with reactive chemical hydrides are avoided, resulting in a more efficient system than those of the prior art that use liquid water.
The electrical power generator of the invention further exemplifies the unique capability of generating electrical power through a passive process, without the need for using pumps or other means of active regulation. It has been unexpected found that the solid chemical fuel inside the power generator creates a region of low humidity hydrogen on the anode side of a PEM fuel cell. The air on the cathode side of the fuel cell is of significantly higher humidity, due to normal ambient air conditions and due to the water produced at the fuel cell cathode by the electrochemical reaction between hydrogen and oxygen. This establishes a concentration gradient which causes water to permeate as water vapor from the more humid cathode side of the fuel cell to the lower humidity hydrogen on the anode side inside the generator cavity to create an equilibrium. Regulation of the hydrogen generation rate is partly self-regulating, because the reaction between hydrogen gas and oxygen gas at the fuel cell produces the required water corresponding to the electrical power generated. A pneumatically controlled valve may further be used to passively adjust the conductance of the water vapor path to the solid fuel.